Young Jun Park

Fiber Supercapacitors Made of Nanowire-Fiber Hybrid Structures for Wearable/Flexible Energy Storage†

many existing energy-harvesting and storage devices are stilltoo bulky and heavy for intended applications. For example,high-efficiency dye-sensitized solar cells (DSSCs) employfluorine-doped tin oxide (FTO) glass as the substrate ofworking electrode. However, the use of rigid FTO glass hasrestricted adaptability of DSSCs during transportation,installation, and application,

Selective dispersion of high purity semiconducting single-walled carbon nanotubes with regioregular poly(3-alkylthiophene)s

Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around SWNTs. However, no sorting of sc-SWNTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-SWNTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-SWNTs. Our approach enables direct film preparation after a simple centrifugation step. Using the sorted sc-SWNTs, we fabricate high-performance SWNT network transistors with observed charge-carrier mobility as high as 12u2009cm(2)u2009V(-1)u2009s(-1) and on/off ratio of >10(6). Our method offers a facile and a scalable route for separating sc-SWNTs and fabrication of electronic devices.

Sound‐Driven Piezoelectric Nanowire‐Based Nanogenerators

Thus, sound power can be used for various novel applications including mobile phones that can be charged during conversations and sound-insulating walls near highways that generate electricity from the sound of passing vehicles. The latter development would have the additional benefi t of reducing noise levels near highways by absorbing the sound energy of vehicles. Here, we report the fi rst power-generating performance of sound-driven nanogenerators based on piezoelectric ZnO nanowires. Figure 1a and b show a schematic diagram of an integrated nanogenerator with piezoelectric ZnO nanowires and a crosssectional fi eld-emission scanning electron microscopy (FE-SEM) image of vertically well-aligned ZnO nanowire arrays (acting as a piezoelectric active layer), respectively. The nanowires were grown using a thermal chemical vapor deposition (CVD) system via a vapor-liquid-solid mechanism on an n-type GaN thin fi lm (acting as a bottom electrode)-deposited sapphire substrate. [ 14 ] It was found that there are no additional peaks other than (0002) and (0004) peaks of ZnO in X-ray diffraction measurements (not shown), indicating good alignment of the ZnO nanowires along the c -axis direction on GaN. A palladium gold (PdAu)coated polyethersulfone (PES) substrate were used as both a top electrode and a vibration plate and placed above the ZnO nanowire arrays. The integrated device was then sealed at the edges to prevent physical and chemical damage. The average length and diameter of the ZnO nanowires were ∼ 10 µ m and ∼ 150 nm, respectively. The integrated nanogenerator was then connected to a measurement system.

Porous PVDF As Effective Sonic Wave Driven Nanogenerators

Piezomaterials are known to display enhanced energy conversion efficiency at nanoscale due to geometrical effect and improved mechanical properties. Although piezoelectric nanowires have been the most widely and dominantly researched structure for this application, there only exist a limited number of piezomaterials that can be easily manufactured into nanowires, thus, developing effective and reliable means of preparing nanostructures from a wide variety of piezomaterials is essential for the advancement of self-powered nanotechnology. In this study, we present nanoporous arrays of polyvinylidene fluoride (PVDF), fabricated by a lithography-free, template-assisted preparation method, as an effective alternative to nanowires for robust piezoelectric nanogenerators. We further demonstrate that our porous PVDF nanogenerators produce the rectified power density of 0.17 mW/cm3 with the piezoelectric potential and the piezoelectric current enhanced to be 5.2 times and 6 times those from bulk PVDF film nanogenerators under the same sonic-input.

Vitrification of fly ash from municipal solid waste incinerator.

Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions. Fly ash can be vitrified by melting at 1500 degrees C for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of approximately 0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ <0.04 ppm, Cr3+ <0.02 ppm, Cu2+ <0.04 ppm and Pb2+ <0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash.

Single‐Fiber‐Based Hybridization of Energy Converters and Storage Units Using Graphene as Electrodes

Recently, there has been great interest in wearable and stretchable energy generation and storage devices utilizing nanotechnology for applications such as self-powering nanosystem that harvests its operating energy from the environment. [ 1 ] Solar, mechanical and thermal energy can be scavenged from the environment using devices that were fabricated using fl exible or stretchable substrates. For example, textile-fi bre-based nanogenerators have been demonstrated utilizing ZnO nanowires (NWs) grown on Kevlar fi bres to scavenge low-frequency mechanical energy. [ 2 ] Twisted fi bre-like electrodes have been used for harvesting solar energy using the dye-sensitized solar cells (DSSCs) approach. [ 3 ] Once the energy is harvested from the environment, an energy storage device is required in order to maintain the operation of the system, but it is usually a separated unit from the energy converters. Flexible batteries. [ 4 ]

Crystalline phase control of glass ceramics obtained from sewage sludge fly ash

Abstract Different types of glasses and glass-ceramics were made using fly ash from sewage sludge incinerators. The optimum nucleation condition was heating at 760xa0°C for 1 h. Crystallization of the nucleated specimen in the region of 1050–1200xa0°C resulted in the formation of two crystalline phases, i.e. anorthite and diopside. The relative fractions of these two phases changed with crystallization temperature. Specimens heat-treated for 2 h at 1050xa0°C consisted mainly of diopside crystals with a minor proportion of anorthite. On the other hand, those heat-treated at 1150xa0°C were primarily composed of anorthite. Glass-ceramics containing large amounts of diopside (1050xa0°C/2 h) generally displayed better physical and chemical properties than their anorthite counterparts (1150xa0°C/3 h) due to the interlocking microstructure of diopside crystals.

Engineering of efficiency limiting free carriers and an interfacial energy barrier for an enhancing piezoelectric generation

The energy harvesting efficiency is of tremendous importance for the realization of a high output-power nanogenerator serving as the basis for self-powered electronics. Here we report that the device performance of a sound-driven piezoelectric energy nanogenerator (SPENG) is remarkably improved by controlling both the carrier density and the interfacial energy in a semiconducting ZnO nanowire (NW), thereby achieving its intrinsic efficiency limits. A SPENG with carrier-controlled ZnO NWs exhibits excellent energy harvesting characteristics with an average power density of 0.9 mW cm−3, as well as a near 50 fold increase in both output voltage and current compared to those of a conventional ZnO NW. In addition, we demonstrate for the first time that an optimized SPENG is large enough and very suitable to drive electrophoretic ink displays based on voltage-drive systems. This fundamental progress makes it possible to fabricate high performance nanogenerators for viable industrial applications in portable/wearable personal electronics such as electronic papers and smart identity cards.

Conversion to glass-ceramics from glasses made by MSW incinerator fly ash for recycling

Glasses were made using fly ash from municipal solid waste (MSW) incinerators with the addition of SiO2, MgO and TiO2. The glasses were then converted to glass-ceramics for further recycling to construction materials. The optimum heat-treatment schedule for the ceramitization of glasses was 720xa0°C for 90 min for nucleation and 870xa0°C for 10 h for crystal growth. Diopside (CaMgSi2O6) was formed as a major crystalline phase. The glass-ceramics showed good mechanical properties with a hardness of 6,730 MPa, fracture toughness of 1.86 Mpa m1/2 and bending strength of 127 MPa. Glasses and glass-ceramics with a composition of 20SiO2–5MgO–75fly ash–2TiO2 (all given in wt.%) showed an excellent resistance against leaching of heavy metal ions in water. The amount of heavy metal ions leached after 18 h at 23xa0°C was well below regulation with Cd2+ <0.04 ppm, Cr3+ <0.004 ppm, Cu2+ <0.03 ppm and Pb2+ <0.15 ppm, respectively.

Highly effective separation of semiconducting carbon nanotubes verified via short-channel devices fabricated using dip-pen nanolithography.

We have verified a highly effective separation of semiconducting single-walled carbon nanotubes (sc-SWNTs) via statistical analysis of short-channel devices fabricated using multipen dip-pen nanolithography. Our SWNT separation technique utilizes a polymer (rr-P3DDT) that selectively interacts with and disperses sc-SWNTs. Our devices had channel lengths on the order of 300-500 nm, with an average of about 3 SWNTs that directly connected the source-drain electrodes. A total of 140 SWNTs were characterized, through which we have observed that all of the SWNTs exhibited semiconducting behavior with an average on/off current ratio of ~10(6). Additionally, we have characterized 50 SWNTs after the removal of rr-P3DDT, through which we have again observed semiconducting behavior for all of the SWNTs with similar electrical characteristics. The relatively low average on-conductance of 0.0796 μS was attributed to the distribution of small diameter SWNTs in our system and due to the non-ohmic Au contacts on SWNTs. The largely positive threshold voltages were shifted toward zero after vacuum annealing, indicating that the SWNTs were doped in air. To the best of our knowledge, this is the first time numerous SWNTs were electrically characterized using short-channel devices, through which all of the measured SWNTs were determined to be semiconducting. Hence, our semiconducting single-walled carbon nanotube sorting system holds a great deal of promise in bringing forth a variety of practical applications in SWNT electronics.